The present invention relates to a board and a method for producing the same. More particularly, the present invention relates to a board on which electronic parts are mounted by using an under-fill material and a method for producing the board.
As a method for mounting electronic parts, for instance, a semiconductor chip on a board such as a wiring board with high density, a flip chip bonding method is known. In the flip chip bonding method, a solder bump is provided on an electrode pad of the semiconductor chip so that the chip is mounted on an electrode pad formed in the board on which the chip is to be mounted so as to be aligned with the electrode of the chip through the solder bump. A gap between the mounted chip and the board is filled with an under-fill material mainly for the purpose of preventing a stress resulting from a difference in coefficient of thermal expansion between the chip and the board from being concentrated to a solder bump connected part. As the under-fill material, a resin including filler such as silica is employed.
The under-fill material is injected to a part between the chip and the board by a capillary action, and then hardened by heating. When the under-fill material is heated, the fluidity of the resin of the under-fill material is increased so that a part of the under-fill material flows outside from the part between the chip and the board. To avoid the insufficiency (causing a void) of the under-fill material with which the part between the chip and the board is filled, the under-fill material is ordinarily somewhat excessively used. This also promotes the outflow of the under-fill material by heating it.
When there is a pad for connecting other parts to the board on the surface of the board on which the chip is mounted, the flowing out under-fill material may possibly reach the area of the pad so that the under-fill material prevents the connection of other parts to the board. In order to meet such a problem, various proposals have been hitherto made. For instance, as disclosed in Patent Document 1, a technique has been known that a dam groove is formed for preventing the expansion of the under-fill material flowing out on a solder resist on which the pad of the board protrudes or a technique that a dam frame for preventing the expansion of the under-fill material is attached to the solder resist in place of the dam groove. As a technique for improving these techniques, the Patent Document 1 discloses a technique that a process (a process for applying another material to the solder resist, a roughening process by applying a laser on the surface of a solder resist, etc.) is carried out so that a part of the surface of the solder resist is apt to readily repel the under-fill material without using the dam groove or the dam frame to prevent the outflow of the under-fill material.
[Patent Document 1] JP-A-2000-164610
In the usual techniques for preventing the under-fill material from flowing out, a part having the under-fill material flowing out from a chip area cannot be used for connecting other parts than the chip. Accordingly, such techniques for preventing the outflow cause a factor of preventing a mounting with a higher density. Further, in the technique for treating the surface of the solder resist, an operation for applying another material or applying the laser is added.